One type of lock assembly of the foregoing kind is an electrically controlled strike assembly generally mounted on or in the frame surrounding the door. In particular the strike assembly is often mounted in a cavity formed in a vertical frame element A bolt, most often a latch bolt, is located on the door so as to engage a strike element, referred to hereinafter as a keeper, of the electric strike assembly when the door is in the closed position. While a handle may be provided, the handle is not operably connected to the latch bolt to enable its retraction to a release position. Instead where the strike assembly is in an unlocked condition the keeper is moved to a release position by the user applying a force to the door, possibly via the handle, to move the door from the closed position. Where the strike assembly is in a locked condition, the user must unlock the strike assembly before the keeper can be moved towards the release position.
The strike assembly includes a locking means which when operable restrains the keeper from moving towards the release position. The locking means generally has a detent which moves along a path from an active position to an inactive position to render the locking means inoperable. In the case of the strike assembly the detent is in the form of one or more pins that are moveable along a path defined by a bore extending between the keeper and a housing supporting the keeper. When the locking means is operable the one or more gins extend across a shear line between the keeper and the housing, to stop the keeper from being moved relative to the housing. An electrical controller, Generally a solenoid or a motor and gearing arrangement, can be utilized to move the one or more pins axially of the bore so that they do not extend across the shear line and thereby render the locking means inoperable.
Other types of lock assembly which are used to secure a door in a closed position include a mortice lock assembly or a rim lock assembly. These types of lock assemblies include a bolt that is movable relative to a housing between an extended locked position and a retracted release position. A hand operable actuator operable by movement of a turn knob or lever is generally used to at least retract the bolt from the extended position. A detent is included that when held in an active position renders the bolt immovable or the actuator inoperable. An electrical controller such as a solenoid or motor and gearing arrangement can be utilized to move the detent along a path from the active position.
A problem can arise when the lock assembly is in a locked condition and a force is applied to the keeper or hand operable actuator urging the keeper or bolt towards a release position before the electrical controller is operated. This is often referred to as preload. Movement of the detent along the path will create friction with the walls defining the path. The output of the electrical controller is generally limited due to size constraints of the lock housing and as a result it can not overcome the frictional forces acting on the detent This results in the detent being stuck in the active position.
It is generally desirable that the electrically controlled lock assembly respond to an electricity supply failure in a manner that suits the location in which the assembly is installed. More specifically in the event of an electricity supply failure it is generally desirable for the lock assembly to be operable in either a fail safe or fail secure mode, so that the locking means is rendered inoperable or operable respectively. It is also generally desirable that the lock assembly be easily adjustable between fail safe and fail secure when being installed.
The above discussion of assemblies and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any of these assemblies formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of this invention.